The present invention relates to threading taps and more particularly to an improved shank which enables the thread tap to be used in for example a three-jaw chuck, a hexagon collet or six or twelve-point sockets and in standard thread tap holders.
Typical threading tape have a cutting section and a shank. The cutting section has cutting edges that cut threads into the wall of a hole as the tap is rotated. The shank has a hardened cylindrical body that ends in a square mounting portion for mounting the tap to a driving means such as a tap handle or tapping machine. The square mounting portion is on the free end of the shank so that a user can apply pressure to the tap with their free hand while rotating the tap handle with their other hand.
With a standard tap, a tap handle or tap machine must be used to engage the four flats of the square mounting portion. Tap handles and mounting fixtures on tapping machines are especially designed to receive the square mounting portion. For example, a tap handle has an open body with two cylindrical handles extending outwardly from opposite sides of the body. A pair of jaws are mounted within the open body. The position with respect to one another is controlled by rotating the tap handles. The square mounting portion of the shank can be positioned between the jaws and the jaws tightened against the square mounting portion to clamp the tap in the tap handle. The tap can then be positioned into a preformed hole and rotated by hand to cut interior threads in the hole.
Tap handles have several disadvantages. Their design makes them difficult to use in tight places because sufficient room is required to rotate the handle which requires an area having a diameter slightly larger than the length of the tap handle measured from handle tip to handle tip. In many applications, this amount of clearance space is not available. Further, threading holes with a tap handle is very slow and great care must be taken to ensure that threads are not crossed.
If mass production is required, a tapping machine must be used. As stated above, tapping machines have special mounting fixtures designed for holding the square mounting portion. There are a variety of holding devices with each designed to clamp onto the square portion at the extreme end of the tap shank while using the cylindrical portion to keep the tap aligned during rotation.
Although tapping machines are much quicker than tap handles, they do have disadvantages. They are not portable. Typically, jobs must be brought to the machine. Thus, any on-site threading of field applications require the use of a tap handle with its inherent restricts on use. Further, tapping machines are extremely expensive and very large, making them impractical for most uses other than mass production requirements.
Other mounting means, such as for example, three-jaw chucks commonly used with drill motors, hexagon collets and six or twelve-point sockets used with standard ratchet wrenches cannot be used to mount and adequately drive a standard tap. Three-jaw chucks and hexagon collets cannot engage the square shank so that the shank will be properly centered, and hardened steel jaws clamped on a hardened cylindrical shank tend to permit slipping under torquing conditions. Six or twelve-point ratchet sockets cannot adequately engage the shank and also tend to permit the tap to slip.
Although the mounting means would greatly enhance the applications and versatility of threading taps, they have generally been avoided because of their inherent disadvantages when used with threading taps.